1. Field of the Invention
The invention relates in general to an output circuit of an integrated circuit, and more particularly to an output circuit capable of steadily outputting a common mode signal and an associated control method.
2. Description of the Related Art
Communications between electronic products may be achieved through physical transmission lines and special communication standards. Differential signals are adopted by many communication standards to achieve quite high communication signal transmission speeds. However, for high-speed communications, transmission lines often require a termination resistor for reducing signal reflection and increasing the transmission speed. For example, in a receiver integrated circuit (or referred to as a sink integrated circuit), a termination resistor is installed and connected between a bonding pad and a power line.
Generally, circuit structures in a common integrated circuit can be functionally divided into two categories—a core circuit and an input/output circuit. The core circuit is in charge of signal processing or conversion in the integrated circuit; the input/output circuit serves as a communication window or bridge between the integrated circuit and external electronic devices. With the progressing evolvement of semiconductor processes and requirements on computation speeds, a core power voltage of the core circuit also continually becomes lower. In response, an input/output circuit needs to have a sufficient driving capability as well as capabilities for matching with external electronic devices. As a result, an input/output power voltage of the input/output circuit is frequently far higher than the core power voltage of the core circuit. For example, an input/output voltage may be maintained at 3.3V, whereas a core power voltage may be as low as 0.9V. When the core power voltage is as low as 0.9V, many unknown and unprecedented issues are incurred. Therefore, there is a need for such issues.